Steelcase and some others, build their chairs just the opposite of most chair manufacturers. Instead of attaching the stem to the caster, they decided to attach the stem to the chair and then designed a caster body to fit the stem on the chair. A normal caster has the stem attached to the caster and then the caster assembly is inserted into a hole in the base of the chair.
There are many caster
manufacturers in the world. There is no standard on how to attach the caster
stem to the caster body. Each manufacturer does it differently. Therefore, the
body from Caster Company A will not fit the body of Caster Company B. This can
present a problem when trying to find a replacement should your caster break.
Sometimes when a caster breaks, it will break away from the stem. When this
happens, it may appear that the stem of the caster is permanently attached to
the chair base. You must look carefully to determine whether it is. If you can
turn the stem with pliers, it will come out. If it will not turn, you must look
Do you know if you really need a stemless caster? See NeedCasters.com for one on the best explanations along with photos.